Apparatus and method for determining a current through a power semiconductor component

ABSTRACT

A circuit configuration includes a power switch and a measuring configuration for detecting the load current through the power switch. The circuit configuration utilizes a voltage drop across a connecting line, in particular a bonding wire, which is connected in series with the power switch for the purpose of determining the load current. A method for determining a current through a power semiconductor component is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of application Ser. No. 10/134,010,filed Apr. 26, 2002; the application also claims the priority, under 35U.S.C. §119, of German patent application No. 101 20 524.4, filed Apr.26, 2001; the prior applications are herewith incorporated by referencein their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a circuit configuration having a powersemiconductor component and an apparatus for determining a currentthrough the power semiconductor component.

FIG. 1 shows a conventional circuit configuration having a powersemiconductor component which is configured as a power switch and isconnected in series with a load, and having a current measuringconfiguration operating according to the so-called current senseprinciple. The power switch T1, configured as an n-channel power MOSFET(Metal Oxide Semiconductor Field Effect Transistor) in FIG. 1, isconnected in series with a load between a first and a second supplypotential V1 V2. In order to detect a load current T1 through powerswitch T1, a second transistor T2 is provided, which is operated at thesame operating point as the power MOSFET T1. In order to set the sameoperating points, the gate connections of the two transistors T1, T2 areconnected to one another and their drain connections are likewiseconnected to one another. In addition, a regulating circuit having anoperational amplifier OP and a third transistor T3 connected in serieswith the second transistor T2 is connected downstream of the sourceconnection of the second transistor T2. Inputs of the operationalamplifier OP are connected to the source connections of the powertransistor and of the second transistor T2, the operational amplifier OPsetting the third transistor T3, which acts as a controllable resistor,in such a way that the source potential of the second transistor T2corresponds to the source potential of the power transistor T1. Acurrent I2 flowing through the second transistor T2 is then proportionalto the load current I1. During the production of the two transistors T1,T2 within the same production process, the proportionality factorcorresponds to the ratio between the active transistor areas of thefirst and second transistors T1, T2.

A measurement voltage UM can be tapped off across a resistor RMconnected in series with the second and third transistors T2, T3,through which resistor the measurement current I2 flows. A connectingterminal of the resistor which is remote from the third transistor T3 isconnected to the second supply potential V2, which is usually areference potential, in particular ground, for an entire circuitconfiguration in which the circuit illustrated is realized. The currentmeasurement signal can then be tapped off relative to the referencepotential V2.

The power switch illustrated in FIG. 1 serves as a so-called high-sideswitch, that is to say as a switch which is connected between thepositive supply potential V1, or the higher positive supply potential,and the load. The generally known measurement principle in accordancewith FIG. 1 cannot be employed, or can only be employed withconsiderable additional outlay, if the power switch serves as low-sideswitch, that is to say if the load is connected between the positivesupply potential and the power switch. The source potential of the powertransistor then approximately corresponds to the reference potential. Inorder that the source potential of the second transistor T2 serving forcurrent measurement is likewise set to the value of the referencepotential, the measuring resistor would have to be connected to apotential which is smaller than the reference potential. The provisionof such a potential, which would have to be negative if the referencepotential is ground, is associated with a considerable outlay oncircuitry.

Furthermore, the measurement principle in accordance with FIG. 1 cannotbe employed, or can only be employed with considerable additionaloutlay, when the potential at the source connection of the power switchbecomes greater than the potential at the drain connection thereof, thatis to say greater than the first supply potential. In this case, itwould likewise be necessary to make available at the source of themeasuring transistor a potential which is greater than the first supplypotential and which would have to be at least as large as a potentialinduced by the inductive load at the source of the first transistor.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a circuitconfiguration having a power semiconductor component, in particular apower switch, and a measuring configuration for detecting a currentthrough the power semiconductor component which overcomes theabove-mentioned disadvantages of the heretofore-known circuitconfigurations of this general type and which is also suitable fordetecting the current in the case of a power switch operated in thereverse direction or as a low-side switch, without additional supplypotentials having to be provided.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a circuit configuration, including:

-   a power semiconductor component having load connections including a    first load connection and a second load connection;-   a connecting line connected between one of the load connections and    one of a load and a terminal for a supply potential;-   the connecting line defining a first node and a second node, the    first node being common to one of the load connections and the    connecting line, the second node being remote from the power    semiconductor component; and-   a measuring configuration having a first terminal and a second    terminal as input terminals, the first terminal of the measuring    configuration being connected to the first node, the second terminal    of the measuring configuration being connected to the second node of    the connecting line.

According to another feature of the invention, the terminal for a supplypotential supplies a first supply potential; and the measuringconfiguration has a third terminal for receiving a second supplypotential.

According to yet another feature of the invention, the connecting linehas a given resistance; the measuring configuration has a series circuitincluding a first resistor and a second resistor; the first resistor hasa resistance, the given resistance of the connecting line and theresistance of the first resistor having a given ratio; the secondresistor is a variable resistor; the terminal for a supply potentialsupplies a first supply potential; and the series circuit is connectedbetween a second supply potential and the second terminal of themeasuring configuration.

According to another feature of the invention, the measuringconfiguration has a series circuit including a first resistor and asecond resistor; and the second resistor is a variable resistor with aresistance set in dependence of a potential difference between the firstterminal of the measuring configuration and a node common to the firstresistor and the second resistor.

According to yet another feature of the invention, the measuringconfiguration has a series circuit including a first resistor and asecond resistor; the connecting line is a first connecting line; and asecond connecting line is connected in series with the first resistor,the second connecting line has a resistance less than a resistance ofthe first resistor.

According to a further feature of the invention, the measuringconfiguration has a series circuit including a first resistor and asecond resistor; and the second resistor is a variable resistorconfigured as a transistor.

Another embodiment according to the invention includes an operationalamplifier having a first input, a second input and an output, the firstinput being connected to the first terminal of the measuringconfiguration, the second input being connected to a node common to thefirst resistor and the second resistor; and the second resistor having acontrol connection, the output of the operational amplifier beingconnected to the control connection of the second resistor.

According to another feature of the invention, the measuringconfiguration has a series circuit including a first resistor and asecond resistor; and the measuring configuration includes a currentmirror configuration which provides a current measurement signaldependent on a current through the first resistor.

According to another feature of the invention, the current mirrorconfiguration provides the current measurement signal with reference toa reference potential.

According to yet another feature of the invention, the powersemiconductor component is a diode.

According to a further feature of the invention, the power semiconductorcomponent is a power transistor with a diode connected in parallelthereto.

With the objects of the invention in view there is also provided, acircuit configuration, including:

-   a power switch having a control connection and load connections;-   a connecting line connected between one of the load connections and    one of a load and a terminal for a first supply potential; and-   a current measuring configuration having a first input terminal, a    second input terminal and a third input terminal, the first input    terminal of the current measuring configuration being connected to a    node common to a first one of the load connections of the power    switch and the connecting line, the second input terminal of the    current measuring configuration being connected to a second one of    the load connections of the power switch, the third input terminal    receiving a second supply potential.

According to another feature of the invention, the power switch is atransistor; and a series circuit includes a measuring transistor and avariable resistor, the series circuit is connected between the secondinput terminal of the current measuring configuration and the thirdinput terminal of the current measuring configuration.

According to yet another feature of the invention, a resistance of thevariable resistor is set in dependence on a potential difference betweenthe first input terminal of the current measuring configuration and anode common to the measuring transistor and the variable resistor.

Another embodiment according to the invention includes an operationalamplifier having a first input, a second input and an output, the firstinput being connected to the first input terminal of the currentmeasuring configuration, the second input being connected to a nodecommon to the measuring transistor and the variable resistor; and thevariable resistor having a control connection, the output of theoperational amplifier being connected to the control connection of thevariable resistor.

According to another feature of the invention, the variable resistor isa transistor.

According to another feature of the invention, the current measuringconfiguration has a current mirror configuration which provides ameasurement signal dependent on a current through the measuringtransistor.

According to another feature of the invention, the current mirrorconfiguration provides the current measurement signal with reference toa reference potential.

According to yet another feature of the invention, the power switch is adiode.

According to a further feature of the invention, the power switch is apower transistor and a diode connected in parallel thereto.

With the objects of the invention in view there is also provided, amethod for determining a current through a power semiconductorcomponent, the method includes the steps of:

-   connecting the power semiconductor component in series with a    connecting line; and-   determining the current through the power semiconductor component by    evaluating a voltage across the connecting line.

The circuit configuration according to the invention has a powersemiconductor component, in particular a power transistor, a diode or aparallel circuit including a power transistor and a freewheeling diode,with a first and a second load connection and a connecting line, theconnecting line being connected between one of the load connections anda load or a terminal for a supply potential. The connecting line is, inparticular, a bonding wire which connects one of the load connections ofthe semiconductor component, which is usually integrated in asemiconductor body, to a connecting pin of a housing in which thesemiconductor body is accommodated. The semiconductor component can beconnected to further circuit components of a circuit via the connectingpin.

In the circuit configuration according to the invention, a voltage dropacross the connecting line, which is brought about by a load currentflowing in the power switch, is used to determine the load current.Alternatively, the voltage drop across the connecting line serves as anadditional auxiliary voltage. To that end, in a first embodiment of theinvention, provision is made of a current measuring configuration havinga first, a second and third input terminal, the first input terminalbeing connected to a node common to the one of the load connections ofthe power semiconductor component and the connecting line, and thesecond connecting terminal being connected to a node of the connectingline which is remote from the power semiconductor component.

In the current measuring configuration, the voltage drop between thefirst and second inputs of the current measuring configuration, that isto say the voltage drop across the connecting line, is determined. Thisvoltage drop is proportional to the load current through the powersemiconductor component, the line resistance of the connecting linecorresponding to the proportionality factor. In the case of bondingwires, the line resistance is dependent on the diameter, length andmaterial thereof. These parameters are usually known precisely, so thatthe line resistance can be determined comparatively exactly and issubject to only small fluctuations from bonding wire to bonding wire inthe same production process on account of the exact and preciselyreproducible production method. Moreover, it is possible, after thecompletion of the semiconductor component to carry out calibration ofthe bonding wire resistance or trimming of the bonding wire resistancewith a known resistor.

In one embodiment of the invention, a series circuit including aresistor whose resistance is in a known ratio to the resistance of theconnecting line/bonding wire is connected between the third connectingterminal, at which a supply potential is available, and the secondconnecting terminal, the resistance of the variable resistor being setin such a way that the voltage drop across the first resistorcorresponds to the voltage drop across the connecting line. The currentflowing through the second resistor is then related to the load currentvia the ratio of the resistances of the connecting line and firstresistor.

The variable resistor is preferably configured as a transistor, anoperational amplifier being provided for driving the transistor oneinput of which operational amplifier is connected to the first inputterminal, the other input of which operational amplifier is connected toa node common to the first and second resistors, and the output of whichoperational amplifier drives the transistor. The use of the operationalamplifier, which has a very low current consumption, enables the settingof the voltage across the second resistor in a manner dependent on theload current virtually without any corruption of the load current.

In a further circuit configuration according to the invention, the powersemiconductor component is configured as a power transistor and ameasuring transistor is provided in the current measuring configuration,the control connection of which measuring transistor is connected to thecontrol connection of the power transistor and one load connection ofwhich measuring transistor is connected to the corresponding loadconnection of the power transistor. In this circuit configurationaccording to the invention, a voltage present on the connecting line ofthe load transistor is utilized for setting the potential at the otherload connection of the measuring transistor to the value of thepotential at the other load connection of the load transistor, withoutan additional supply potential being necessary.

The present invention can be employed in particular in circuitconfigurations in which the power semiconductor component is configuredas a transistor and is used as a high-side switch or as a low-sideswitch. However, the invention can also be used in connection with othersemiconductor components which enable a current flow between twoconnecting terminals and which are integrated in a semiconductor bodywhich is contact-connected through the use of a bonding wire.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin an apparatus and a method for determining the current through a powersemiconductor component, it is nevertheless not intended to be limitedto the details shown, since various modifications and structural changesmay be made therein without departing from the spirit of the inventionand within the scope and range of equivalents of the claims.

The construction and a method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a conventional circuit configurationhaving a current measuring configuration operating according to thecurrent sense principle;

FIG. 2 is a circuit diagram of a circuit configuration according to theinvention having a power semiconductor component, a connecting lineconnected in series with the power semiconductor component, and having acurrent measuring configuration in accordance with a first functionalprinciple;

FIG. 3 is a circuit diagram of a circuit configuration having ann-channel field-effect transistor as a low-side switch and a currentmeasuring configuration in accordance with the first functionalprinciple which detects a current which is positive in the drain-sourcedirection of the field-effect transistor;

FIG. 4 is a circuit diagram of a circuit configuration according to theinvention having an n-channel field-effect transistor and a currentmeasuring configuration in accordance with the first functionalprinciple which detects a current which is negative in the drain-sourcedirection of the field-effect transistor;

FIG. 5 is a circuit diagram of a circuit configuration according to theinvention having an n-channel field-effect transistor as a high-sideswitch and a current measuring configuration in accordance with thefirst functional principle which detects a current which is positive inthe drain-source direction of the field-effect transistor;

FIG. 6 is a circuit diagram of a circuit configuration according to theinvention having a p-channel field-effect transistor as a high-sideswitch and a current measuring configuration in accordance with thefirst functional principle which detects a current which is positive inthe source-drain direction of the field-effect transistor;

FIG. 7 is a circuit diagram of a circuit configuration according to theinvention having a p-channel field-effect transistor as a high-sideswitch and a current measuring configuration in accordance with thefirst functional principle which detects a current which is negative inthe source-drain direction of the field-effect transistor;

FIG. 8 is a circuit diagram of a circuit configuration according to theinvention having a power switch, a connecting line connected in serieswith the power switch, and a current measuring configuration inaccordance with a second functional principle;

FIG. 9 is a circuit diagram of a circuit configuration according to theinvention having an n-channel field-effect transistor as a low-sideswitch and a current measuring configuration in accordance with thesecond functional principle which collects a current which is positivein the drain-source direction of the field-effect transistor;

FIG. 10 is a circuit diagram of a circuit configuration according to theinvention having an n-channel field-effect transistor as a high-sideswitch and a current measuring configuration in accordance with thesecond functional principle which detects a current which is negative inthe drain-source direction of the field-effect transistor; and

FIG. 11 is a circuit diagram of a circuit configuration according to theinvention having a p-channel field-effect transistor as a high-sideswitch and a current measuring configuration in accordance with thesecond functional principle which detects a current which is positive inthe source-drain direction of the field-effect transistor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the figures, unless specified otherwise, identical reference symbolsdesignate identical or corresponding parts, currents and voltages. FIG.2 shows a first exemplary embodiment of a circuit configurationaccording to the invention, which has a power switch which is configuredas an n-channel field-effect transistor NTL and whose gate connection Gforms a control connection, whose drain connection D forms a first loadconnection and whose source connection S forms a second load connectionof the power switch. The drain-source path D-S of the transistor NTL isconnected in series with a connecting line BL between a first connectionLF and a second connection P1. The connecting line BL has a lineresistance RBL, which is illustrated as an ohmic resistor RBL in FIG. 2.The connecting line BL is, in particular, a bonding wire which connectsthe source region of the transistor NTL integrated in a semiconductorbody to a connecting pin of a housing (not illustrated) in which thesemiconductor body with the power transistor NTL is accommodated. Theconnecting pin corresponds to the second connecting terminal P1 in FIG.2. The drain region of a power transistor accommodated in a housing isusually connected directly to the lead frame of the housing. The firstconnecting terminal LF in FIG. 2 represents the lead frame of such ahousing. If a load current IL flows through the power transistor NTL,then this load current IL brings about a voltage drop UBL across theconnecting line BL, which voltage drop is evaluated in a currentmeasuring configuration MA1 connected to the connecting line BL. Avoltage drop across the connecting line BL is brought about irrespectiveof whether the load current IL, with the power transistor TL beingdriven, flows through the drain-source path D-S of the power transistorNTL in the direction depicted in FIG. 1 or whether the current flows inthe opposite direction via a freewheeling diode DF, which is connectedin parallel with the drain-source path D-S and which is integrated inthe power transistor NTL. A voltage drop UBL across the connecting lineBL is negative in the case of a current flow via the freewheeling diodeDF, that is to say a current flow counter to the direction depicted.

The current measuring configuration MA1 has a first connecting terminalK1, which is connected to the source connection S of the powertransistor NTL, or to the node common to the power transistor NTL andthe connecting line BL. A second connecting terminal K2 is connected tothat connection of the connecting line BL which is remote from the powertransistor NTL. The current measuring configuration MA1 has a seriescircuit including a first resistor RS, whose resistance is in a knownratio to the resistance RBL of the connecting line BL, and a variablesecond resistor, which is configured as transistor T1 in FIG. 2.Moreover, in the exemplary embodiment, a second connecting line BS isprovided, which, in particular, is likewise configured as a bonding wireand which connects the first resistor RS via the second connectingterminal K2 to the first connecting line BL, or the connecting pin P1.In the exemplary embodiment, the transistor T1 serving as variableresistor is configured as a p-channel transistor whose drain connectionis connected to the first resistor RS and whose source connection S isconnected to a third connecting terminal P2 of the current measuringconfiguration MA1. An operational amplifier OP1 is provided for drivingthe transistor T1, the noninverting input of which operational amplifieris connected to the first input terminal K1 and the inverting input ofwhich operational amplifier is connected to the node N1 common to theresistor RS and the transistor T1. The operational amplifier OP1 setsthe on resistance of the transistor T1 in such a way that a potentialdifference U1 between the first input terminal K1 and the common node N1is zero, the sum of a voltage URS across the first resistor RS and avoltage UBS across the second connecting line BS then corresponding tothe voltage UBL across the first connecting line BL. The value of thefirst resistor RS is preferably significantly greater than theresistance of the first connecting line RBL. The value of the firstresistor RS is furthermore significantly greater than the resistance ofthe second connecting line BS, the voltage drop URS brought about by acurrent IRS through the first resistor RS then being significantlygreater than the voltage drop UBS across the second connecting line BS,so that the voltage drop across the second connecting line BS can bedisregarded. The voltage URS across the first resistor RS corresponds atleast approximately to the voltage UBL on the connecting line BL, i.e.:URS=UBL.The following then holds true for the current IRS through the firstresistor RS:IRS=(RBL/RS)·IL.

The current IRS through the first resistor is thus proportional to theload current IL, the proportionality factor corresponding to the knownratio of the resistances of the first resistor RS and the connectingline BL. Given a known resistance of the second bonding wire BS, whichcan likewise be determined from the parameters such as length, diameterand composition, the sum of the resistance of the second bonding wire BSand the resistance of the resistor RS can also be taken into account ina known manner in the above relationship for determining the loadcurrent IL from the measurement current IRS.

In a further embodiment, it is provided that, whilst dispensing with aseparate resistor, the bonding wire BS forms the first resistor throughwhich the measurement current flows and across which there is a voltageproportional to the load current. In order to satisfy the abovementionedcondition wherein the resistance of the first resistor is greater thanthe resistance of the bonding wire BL in series with the semiconductorcomponent, the diameter of the bonding wire BS is chosen to be smallerthan that of the bonding wire BL or the bonding wire BS is chosen to belonger than the bonding wire BL.

This current IRS, which is proportional to the load current IL, can bedetected through the use of evaluation circuits explained in more detailbelow and be used for providing a current measurement signal, inparticular for providing a voltage referred to reference potential ascurrent measurement signal.

If, in the circuit configuration illustrated in FIG. 2, the potential atthe connecting terminal LF is greater than at the connecting terminalP1, then the current IL flows in the direction depicted in FIG. 2. Inorder to bring about a voltage drop URS across the first resistor RSwhich essentially corresponds to the voltage drop UBL across theconnecting line, the connecting terminal P2 of the current measuringconfiguration MA1 must likewise be connected to a potential which isgreater than the potential at the connecting terminal P1. In this case,the connecting terminal P2 is preferably connected to the connection LF,or the drain connection of the load transistor NTS.

If the potential at the connecting terminal P1 is greater than at theconnecting terminal LF, then the transistor NTL is operated in thereverse direction and the connection P2 must be connected to a potentialwhich is less than the potential at the connecting terminal P1, in orderto bring about a voltage drop URS across the first resistor RS whichcorresponds to the voltage UBL across the connecting line BL. To thatend, the connection P2 of the current measuring configuration MA1 can beconnected to the drain connection D of the power transistor NTL in thiscase as well.

The functional principle of the current measuring configurationillustrated in FIG. 2, which is based on detecting the voltage dropacross the bonding wire connected in series with the semiconductorcomponent, is independent of the semiconductor component used. Insteadof the transistor or a transistor with a parallel freewheeling diode, itis possible to use any other semiconductor component desired, forexample a diode, which permits a current flow in one of the directionsbetween the connections LF and P1, the specific configuration of thecurrent measuring configuration depending on the direction of theflowing current, as is explained below using various examples withcurrent measuring configurations which are based on the functionalprinciple described.

Consequently, the current measuring configuration illustrated in FIG. 2can be used for determining a load current IL through a powersemiconductor component, in particular a power transistor NTL, both whenthe transistor is used as a high-side switch and when the transistor isused as a low-side switch, independently of whether the power transistoris configured as an n-conducting transistor or as a p-conductingtransistor. The current measuring configuration MA1 is also suitable fordetermining a current which flows through the power transistor NTL inthe reverse direction.

Both the resistance of the resistor RS and the resistance of the bondingwire usually vary with temperature. In order largely to prevent thistemperature dependence from affecting the measurement result, oneembodiment of the invention provides for the resistor RS and the bondingwire to be provided such that they are spatially closely adjacent to oneanother, so that they are subject to the same temperature influences.

FIGS. 2 to 7 show exemplary embodiments of circuit configurationsaccording to the invention in which n-conducting power transistors orp-conducting power transistors which are connected up as high-sideswitches or low-side switches are used as power semiconductorcomponents. The circuit configurations each have a current measuringconfiguration MA1 which functions according to the first functionalprinciple explained with reference to FIG. 2 and which is coordinatedwith the respective conduction type of the power transistor and theconnections thereof, each of the current measuring configurations havinga basic circuit in accordance with FIG. 2. The reference symbol NTLhereinafter designates an n-conducting power transistor and thereference symbol PTL designates a p-conducting power transistor. Thereference symbols RS for the first resistor, OP1 for the operationalamplifier, T1 for the variable resistor, K1, K2, P2 for the inputs ofthe current measuring configuration, P1, LF for the connections of theseries circuit including power transistor NTL and connecting line BL andMA1 for the current measuring configuration are retained below,independently of whether further circuit components are present in thecurrent measuring configuration MA1.

FIG. 3 shows an exemplary embodiment of a circuit configurationaccording to the invention with an n-conducting field-effect transistorNTL as power transistor, which is connected in series with a load RL andthe connecting line BL between a connecting terminal for a first supplypotential Vbb and a reference potential M. The power transistor NTL actsas a low-side switch, i.e. the load RL is connected between the positivesupply potential Vbb and the drain connection D of the power transistorNTL, or the connecting terminal LF. Furthermore, a load current IL flowsthrough the power transistor in the direction depicted. This loadcurrent is positive with respect to the drain-source direction, that isto say the potential at the drain connection D, or the connectingterminal LF, is greater than at the source connection S.

The second connecting terminal P1 of the series circuit including powertransistor NTL and connecting line BL is connected to the referencepotential M. In addition to the series circuit—already explainedabove—including the first resistor RS and the variableresistor—configured as transistor T1—and the operational amplifier OP1,the current measuring configuration MA1 has a current mirrorconfiguration which maps a current IRS flowing through the firstresistor RS onto a measurement current IM, the measurement current IMbringing about a voltage drop UM relative to reference potential Macross a current measuring resistor RM. The transistor T1 serving asvariable resistor is configured as a p-channel transistor whoseresistance is set through the use of the operational amplifier OP1 insuch a way that the voltage drop URS across the first resistor RSapproximately corresponds to the voltage drop UBL across the connectingline BL. The third input P2 of the current measuring configuration MA1is connected to the positive supply potential Vbb in order to bringabout a voltage drop URS across the first resistor RS corresponding tothe voltage drop UBL across the connecting line BL.

The current mirror configuration has a transistor T3, whose sourceconnection S is connected to the source connection S of the transistorT1, whose gate connection G is connected to the gate connection of thetransistor T1. Connected downstream of the transistor T3 is a furthertransistor T4, which is likewise configured as a p-channel transistorand which is driven by an operational amplifier OP4, whose noninvertinginput is connected to the drain connection D of the transistor T1 andwhose inverting input is connected to the drain connection of thetransistor T3. The on resistance of the transistor T4 is set through theuse of the operational amplifier OP4 in such a way that the drainpotentials of the transistors T1, T3 match, so that the two transistorsT1, T3 are operated at the same operating point. Given identicaltransistors T1, T3, a current IM flowing through the transistor T3corresponds to the current IRS through the first resistor RS. If thetransistors T1, T3 differ in their active transistor areas—but they areotherwise constructed identically—then the current IM is proportional tothe current IRS, the proportionality factor corresponding to the ratioof the active transistor areas between the transistor T3 and thetransistor T1. The following then holds true for the voltage UM whichcan be tapped off relative to reference potential M and represents acurrent measurement signal:UM=RM·IM=RM·IRS=RM·(RBL/RS)·IL,if IRS=IM holds true. If the transistors T1 and T3 have different activetransistor areas, an additional proportionality factor must be takeninto account in a known manner.

Consequently, the circuit configuration according to the invention asshown in FIG. 3 makes it possible to provide a current measurementsignal dependent on the load current IL in the case of a powertransistor NTL used as a low-side switch by evaluation of the voltageUBL present across the bonding wire BL, without a negative auxiliaryvoltage being required.

FIG. 4 shows a further exemplary embodiment of a circuit configurationaccording to the invention, in which an n-conducting field-effecttransistor used as a switch is connected, in a manner not specificallyillustrated, to a voltage source and a load in such a way that anegative voltage UL is present between the connecting terminal LF andthe connecting terminal P1. Consequently, a potential which is less thanthe potential at the connection P1 is present at the drain connection Dof the power transistor NTL, so that the load current IL illustrated inFIG. 4 is likewise negative relative to the drain-source direction, thatis to say flows counter to the direction depicted. The construction ofthe current measuring configuration MA1 corresponds to the constructionof the current measuring configuration MA1 described in FIG. 3, thetransistor T1 used as a variable resistor and the associated currentmirror transistor T3 and the transistor T4 being configured as n-channeltransistors. A measurement current IM flows through the measuringresistor RM, which measurement current is dependent on the load currentIL in the manner explained above, the measurement current IM also beingnegative in the exemplary embodiment in accordance with FIG. 4. In orderto provide a measurement current IM which is positive relative toreference potential M, it is possible to provide a further currentmirror configuration in a generally known manner.

The third connecting terminal L1 of the current measuring configurationMA1 in accordance with FIG. 4, to which the source connections of thetransistors T1, T3 are connected, is connected to the drain connection Dof the power transistor NTL in order to put the source connections S ofthe transistors T1, T3 at the negative supply potential brought about bythe load R, L.

If a positive or a negative load current through the power transistor isbrought about by a load in a manner dependent on the operating statethereof, then it is possible, in a manner not specifically illustrated,for the current measuring configurations according to FIGS. 2 and 3simultaneously to be connected to the transistor and the connecting linein the manner described in these figures, in order to be able to detectboth positive and negative load currents.

Thus, a circuit configuration combined through the circuitconfigurations in accordance with FIGS. 3 and 4 can be used for exampleas an “intelligent connecting terminal” of a vehicle battery, that,depending on whether the battery is connected to a load for the purposeof outputting current or to a charging circuit for the purpose of takingup current, accordingly has a positive or negative current flowingthrough it.

Load currents with alternating directions can occur for example wheninductive loads are driven through the use of a transistor and afreewheeling diode in parallel with the transistor. In applications ofthis type, a load current flows through the inductive load when thetransistor is in the on state, in which case, after the transistor turnsoff, the freewheeling diode accepts a current which is induced by theinductive load and flows in the opposite direction to the load current.Load currents with alternating directions can also occur for example inswitches which are configured to connect a load to voltages with avariable sign. Such a switch may serve for example for connecting abattery, in particular a vehicle battery, either to a load, which drawscurrent form the battery, or to a charging unit, which feeds current tothe battery, in which case the current respectively flowing is to bedetermined.

FIG. 5 shows a further exemplary embodiment of a circuit configurationaccording to the invention with a power switch which is configured as ann-conducting field-effect transistor NTL and is used as a high-sideswitch, the drain connection D of the power transistor NTL beingconnected to the positive supply potential Vbb and a load RL beingconnected in series with the connecting line BL between the secondconnection P1 and reference potential M.

The construction and the method of operation of the current measuringconfiguration MA1 in accordance with FIG. 5 corresponds to theconstruction and the method of operation of the current measuringconfiguration in accordance with FIG. 3, the source connections of thep-channel transistors T1, T3 being connected to the positive supplypotential Vbb via the third connecting terminal P2 of the currentmeasuring configuration MA1.

FIG. 6 shows a further exemplary embodiment of a circuit configurationaccording to the invention, in this circuit configuration a p-conductingfield-effect transistor PTL being used as a power switch, which servesas a high-side switch in the exemplary embodiment in accordance withFIG. 6. The source connection S of the transistor PTL is connected tothe positive supply potential Vbb via the connecting line BL and thesecond connection terminal P1. The load RL is connected to the drainconnection D or the first connection LF, which usually corresponds tothe lead frame of a housing, the other connecting terminal of the loadbeing connected to reference potential M.

The variable resistor T1 connected in series with the first resistor RSis configured as a p-conducting field-effect transistor whose sourceconnection S is connected to the first resistor RS and whose drainconnection is connected to the third connecting terminal P2 of thecurrent measuring configuration MA1. A current measuring resistor RM isconnected between the third connecting terminal P3 and referencepotential M, across which resistor a current measurement signal UM canbe tapped off which is proportional to the current IRS through the firstresistor RS, or proportional to the load current IL. The voltage UBLacross the connecting line BL and thus the voltage URS across the firstresistor RS are positive in the exemplary embodiment in accordance withFIG. 6 and the load current IL and, respectively, the current IRSthrough the first resistor RS are likewise positive.

FIG. 7 shows a circuit configuration according to the invention with ap-conducting field-effect transistor as a power switch, which serves asa high-side switch in the exemplary embodiment, it being assumed in theexemplary embodiment that the load connected between the firstconnecting terminal LF and reference potential brings about, at thefirst connecting terminal LF, a potential which is greater than thepositive supply potential Vbb to which the first connecting terminal P1of the series circuit including power transistor and connecting line BLis connected.

The second connecting terminal P2 of the current measuring configurationMA1 is connected to the drain connection of the power transistor in theexemplary embodiment. The load current IL flows counter to the directiondepicted in FIG. 7, in which case, with the transistor PTL being driven,the load current flows via the source-drain path of the power transistorPTL and otherwise via the freewheeling diode DF. The current through thefirst resistor RS likewise flows counter to the direction depicted inFIG. 7, the first transistor T1, which serves as a variable resistor,being configured as a p-conducting transistor whose drain connection Dis connected to the first resistor RS and whose source connection S isconnected to the third connecting terminal P3 of the current measuringconfiguration. A current mirror configuration having a transistor T3, atransistor T4 serving as a variable resistor, and an operationalamplifier OP4 maps this negative current IRS through the first resistorRS onto a measurement current IM which is positive relative to referencepotential M. To that end, the gate connection of the third transistor T3is connected to the gate connection of the first transistor T1, and thesource connection of the transistor T3 is connected to the sourceconnection of the first transistor T1. The transistor T4 is driven by anoperational amplifier OP4, whose noninverting input is connected to thedrain connection of the transistor T1 and whose inverting input isconnected to the drain connection D of the transistor T3. The transistorT4 sets the drain potential of the transistor T3 in such a way that thisdrain potential matches the drain potential of the transistor T1, sothat the transistors T1 and T3 are operated at the same operating point,so that the measurement current IM corresponds to the magnitude of thecurrent IRS through the first resistor RS, or that the measurementcurrent IM is related to the current IRS through the first resistor RSor the load current IL by way of the area ratio of the two transistorsT1, T3.

FIG. 8 shows a circuit configuration with a power semiconductorcomponent as power transistor. The power transistor being connected inseries with a connecting line BL and a current measuring configurationMA2 being provided, which functions in accordance with a secondfunctional principle. As in the exemplary embodiments described above,the drain-source path of the transistor TL is connected in series with aconnecting line BL, the series circuit being connected up between afirst terminal LF, to which the drain connection D of the powertransistor NTL is connected, and a second terminal P2, to which aconnection of the connecting line BL is connected.

The current measuring configuration MA2 has a measuring transistor NTS,which is of the same conduction type as the power transistor NTL, thedrain connection D of the measuring transistor NTS being connected tothe drain connection D of the power transistor NTL via a connectingterminal K5 of the current measuring configuration MA2. The gateconnection G of the measuring transistor NTS is connected to the gateconnection of the load transistor NTL.

The power transistor NTL and the measuring transistor NTS are preferablyintegrated in a common semiconductor body. This capitalizes on the factthat power transistors usually include a multiplicity of identicallyconstructed transistor cells, one or a number of these transistor cellswhose source connections are not connected to the source connections ofthe remaining transistor cells being utilized in the measuringtransistor NTS.

The current measuring configuration MA2 furthermore has a variableresistor which, in the exemplary embodiment, is configured as atransistor T2 and is connected in series with the measuring transistorNTS. This transistor T2 is driven by an operational amplifier OP2, whosenoninverting input is connected to the source connection S of the powertransistor NTL via a connecting terminal K4 and whose inverting input isconnected to a node common to the current measuring transistor NTS andthe variable resistor T2. The operational amplifier OP2 sets the onresistance of the transistor T2 in such a way that the source potentialsof the load transistor NTL and of the measuring transistor NTS match.These two transistors are then operated at the same operating point, thedrain-source voltage UDSL of the power transistor NTL corresponding tothe drain-source voltage UDSS of the measuring transistor NTS. A sourcecurrent ITS flowing through the measuring transistor NTS is thenproportional to a load current IL flowing through the power transistorNTL, the proportionality factor corresponding to the ratio between theactive transistor area of the load transistor NTL and the activetransistor area of the power transistor NTS.

The functional principle of the measuring configuration MA2 is based onoperating the measuring transistor NTS at the same operating point asthe load transistor, the voltage drop across the bonding wire BL servingfor setting the source potential of the measuring transistor NTS.

FIG. 9 shows a circuit configuration with an n-conducting powertransistor NTL serving as a low-side switch, the drain connection of thepower transistor NTL being connected to a load RL and that connection ofthe load RL which is remote from the power transistor NTL beingconnected to the positive supply potential Vbb. The second connection P1of the series circuit including load, power transistor NTL andconnecting line BL is connected to reference potential M. In theexemplary embodiment, the transistor T2, which serves as a variableresistor and is driven by the operational amplifier OP2, is configuredas an n-conducting transistor whose drain connection D is connected tothe source connection S of the measuring transistor NTS and whose sourceconnection is connected to the third connecting terminal P3 of thecurrent measuring configuration MA2. In the exemplary embodiment, thethird connecting terminal P3 is connected to reference potential M via asecond connecting line BS2, in particular a bonding wire. Theconfiguration including operational amplifier OP2 and transistor T2 setsthe source potential S of the measuring transistor NTS in such a waythat it corresponds to the source potential of the power transistor NTL.The source current ITS flowing through the measuring transistor is thenproportional to the load current IL. The measurement current ITS isusually significantly smaller than the load current IL, so that thevoltage UBS2 dropped across the second connecting line BS2 issignificantly less than the voltage UBL across the connecting line BL.The difference formed from the voltage UBL and the voltage UBS2 isobtained as drain-source voltage of the transistor T2 and serves forsetting the source potential of the measuring transistor NTS to thesource potential of the transistor NTL. The measurement current ITS canbe tapped off through the use of a current mirror configuration, whichis not explicitly illustrated in FIG. 9 but is generally known to aperson skilled in the art, and can be converted into a voltage referredto reference potential M, which voltage serves as current measurementsignal, as is explained using the two exemplary embodiments below inFIGS. 11 and 12.

FIG. 10 shows a further exemplary embodiment of a circuit configurationaccording to the invention, in which an n-conducting field-effecttransistor TL serves as a high-side switch. The drain connection D ofthe field-effect transistor is connected to the first connection LF orto the positive supply potential Vbb. The second connection P1 of theseries circuit including power transistor TL and connecting line BL isconnected to a load R, L, whose connection remote from the connectingline BL is connected to reference potential M. In the exemplaryembodiment, the third connecting terminal P3 of the current measuringconfiguration MA2 is connected via a second connecting line BS2 to thesecond connecting terminal P1, which is, for example, a connecting pinof a housing in which the power transistor TL and the current measuringconfiguration MA2 are integrated. In this case, the power transistor TLand the current measuring configuration MA2 are usually integrated in acommon semiconductor body.

In the exemplary embodiment, the transistor T2, which serves as avariable resistor and is connected in series with the measuringtransistor TS, is configured as a p-conducting field-effect transistorwhose drain connection is connected to the source connection S of themeasuring transistor T5 and whose source connection is connected to thethird connecting terminal P3.

A current mirror configuration having a transistor T5, a transistor T6and an operational amplifier OP6 serves for converting the measurementcurrent ITS through the measuring transistor TS into a measurementcurrent IM which is positive relative to reference potential M. Thecurrent mirror configuration has a p-conducting transistor T5, whosegate is connected to the gate of the transistor T2 and whose source isconnected to the source of the transistor T2. A transistor T6 isconnected in series with the transistor T5 and is driven by anoperational amplifier OP6, the operational amplifier OP6 driving thetransistor T6 in such a way that the source potential of the transistorT5 corresponds to the source potential of the transistor T2. Thetransistors T2, T5 are then operated at the same operating point, themeasurement current IM being related to the measurement current ITSthrough the measuring transistor TS by way of the area ratio of the twotransistors T2, T5. The current measuring configuration in accordancewith FIG. 10 is configured to detect a negative load current IL, i.e. aload current which flows counter to the direction depicted in FIG. 10.Such a load current is produced if the potential at the connectingterminal P1 is greater than the supply potential Vbb at the connectingterminal LF.

FIG. 11 shows an exemplary embodiment of a circuit configuration with ap-conducting transistor, which is used as a high-side switch. The sourceconnection S of the transistor PTL is connected to the positive supplypotential Vbb via the connecting line BL. The load RL is connectedbetween the drain connection D of the power transistor PTL and referencepotential M. The third connecting terminal P3 of the current measuringconfiguration MA2 is connected to the positive supply potential Vbb viathe second connecting line BS2. In the exemplary embodiment, thetransistor T2 serving as a variable resistor is configured as ap-channel transistor whose source connection is connected to supplypotential Vbb via the connecting line BS2 and whose drain connection Dis connected to the drain connection D of the measuring transistor TS,which is likewise configured as a p-conducting transistor. If apotential which is greater than the potential at the connecting terminalLF is present at the connecting terminal P1, then a load current ILflows through the power transistor PTL, which load current flows in thedirection depicted in FIG. 11. The measuring transistor TS is operatedat the same operating point as the load transistor PTL and themeasurement current flowing through the measuring transistor TS flows inthe direction depicted in FIG. 11. A current mirror configuration havinga transistor T5, a transistor T6 and an operational amplifier OP6converts the measurement current ITS into a measurement current IM whichis positive relative to reference potential M and brings about apositive voltage drop UM relative to reference potential M in ameasuring resistor RM connected downstream of the transistors T5, T6,the voltage drop UM being proportional to the measurement current ITSthrough the transistor TS, or proportional to the load current IL.

The concept underlying the circuit configurations according to theinvention is based on detecting the voltage drop UBL brought about by aload current on a connecting line, usually a bonding wire, eitherthrough the use of a measuring resistor in a current measuringconfiguration, and providing a suitable current measurement signal, orusing the voltage drop across the connecting line to set a measuringtransistor to the same operating point as the load transistor. Furtherexternal supply potentials are not necessary for this purpose.

1. A circuit configuration, comprising: a power switch having a controlconnection and load connections, said power switch being a transistor; abonding wire connected between one of said load connections and one of aload and a terminal for a first supply potential; and a currentmeasuring configuration indicating a current flowing through said powerswitch by using a potential at said bonding wire, said current measuringconfiguration having a first input terminal, a second input terminal anda third input terminal, said first input terminal of said currentmeasuring configuration being connected to a node common to a first oneof said load connections of said power switch and said bonding wire,said second input terminal of said current measuring configuration beingconnected to a second one of said load connections of said power switch,said third input terminal receiving a second supply potential; saidcurrent measuring configuration including a series circuit having ameasuring transistor with a drain-source path and a variable resistorconnected in series with said load path of said measuring transistor,said series circuit is connected between said second input terminal ofsaid current measuring configuration and said third input terminal ofsaid current measuring configuration.
 2. The circuit configurationaccording to claim 1, wherein a resistance of said variable resistor isset in dependence on a potential difference between said first inputterminal of said current measuring configuration and a node common tosaid measuring transistor and said variable resistor.
 3. The circuitconfiguration according to claim 1, including: an operational amplifierhaving a first input, a second input and an output, said first inputbeing connected to said first input terminal of said current measuringconfiguration, said second input being connected to a node common tosaid measuring transistor and said variable resistor; and said variableresistor having a control connection, said output of said operationalamplifier being connected to said control connection of said variableresistor.
 4. The circuit configuration according to claim 1, whereinsaid variable resistor is a transistor.
 5. The circuit configurationaccording to claim 1, wherein said current measuring configurationfurther includes a current mirror configuration which provides ameasurement signal dependent on a current through said measuringtransistor.
 6. The circuit configuration according to claim 5, whereinsaid current mirror configuration provides the current measurementsignal with reference to a reference potential.
 7. The circuitconfiguration according to claim 1, further comprising a diode connectedin parallel with said power switch.
 8. The circuit configurationaccording to claim 1, wherein said power switch includes a drain-sourcepath, said drain-source path has a first end that is connected to saidfirst one of said load connections of said power switch, and saiddrain-source path has a second end that is opposite said first end andthat is connected to said second one of said load connections of saidpower switch.